1. Field of the Invention
The present invention relates in general to dynamo-electric machines and more particularly to the dynamo-electric machines of a type that is equipped with a single stator and double rotors and operated with a compound current.
2. Description of the Related Art
Japanese Laid-open Patent Application (Tokkaihei) 11-356015 shows a so-called dynamo-electric machine that is operated with a compound current. The dynamo-electric machine shown by the publication is of a single stator double rotor type including a single stator and inner and outer rotors that are coaxially arranged to form a three-layer construction. Each rotor is equipped with a plurality of permanent magnets that are circumferentially arranged at evenly spaced intervals. At least one of the inner and outer rotors is equipped with an induction coil. The stator is provided with a single coil to which a compound current is applied to generate rotating magnetic fields of which number is the same as that of the rotors. With such arrangement, a rotation of the inner rotor and that of the outer rotor can be independently controlled with a small loss of electric current.